Copy head (r256279) to stable/10 as part of the 10.0-RELEASE cycle.

Approved by: re (implicit)
Sponsored by: The FreeBSD Foundation

Xref altq(4) for drivers that support it according to altq(4).

- For the sake of completeness mention back-end support for the ILACC
and add a list of known-working PCI devices.
- For consistency throughout this man page also talk about C-Bus and
ISA adapters rather than cards.
- Add missing .Tn.
- Mention ifconfig(8) along with listing selectable media types.
- Add/un-comment hardware notes for the newly supported 'lebuffer'
variants (the transition from P/N 501-1860 to 501-1869 isn't a typo).

Add Allied Telesyn AT-1500 (logical ID ATK1500, compat ID PNP828C)
to the list of known working ISA PnP cards.

Reported by: Gheorghe Ardelean

Revise markup.

- Talk about chips rather than chip sets as AMD LANCE and PCnet are
single-chip.
- Add some more rationale about le(4).
- Add/un-comment hardware notes for C-Bus and ISA adapters.

Correct and improve the description of le(4) vs. pcn(4); apparently I
was thinking from the pcn(4) perspective instead of the le(4) one when
writing the former version as le(4) supports a superset of the chips
supported by pcn(4) and not the other way round.

Add a man page for le(4), based on the NetBSD one.